1. Field of the Invention
The present invention relates to an automotive automatic transmission in which two transmission mechanisms are connected together.
2. Description of the Related Art
JP-B-5-67831 describes an example of such an automatic transmission.
The example is an automatic transmission wherein a primary transmission in which a plurality of gear shift conditions are changed over and a sub-transmission in which a high-speed condition and a low-speed condition are changed over are connected to each other in series, whereby a multiplicity of change-speed gears are established by combinations of respective gear shift conditions of both of the transmissions.
In shifting the gears, there is a case where the two transmissions are made to change the gears in directions opposite to each other.
For example, in order to upshift gears of the overall transmission by one gear toward a high-speed side, there occurs a case where the primary transmission is upshifted whereas the sub-transmission is downshifted. However, in the event that change-gear timings of the primary transmission and the sub-transmission overlap or deviate excessively in the opposite direction, a good drive feeling cannot be obtained.
To cope with this, the example described in the above publication includes an opposite direction gear shift detecting means, a delay-time setting means and a gear shift comment outputting means. The opposite direction gear shift detecting means detects a gear shift condition in which the two transmissions are made to shift gears in the opposite direction to each other in shifting gears. The delay-time setting means sets a delay time for delaying the gear shift of one of the two transmissions relative to the gear shift of the other based on predetermined conditions when such an opposite direction gear shift is carried out. The gear shift command outputting means outputs a gear shift execution command to one of the two transmissions, and then, outputs a gear shift execution command to the other transmission after the delay time so set has elapsed. With this construction, the deterioration of the drive feeling is prevented by delaying the gear shift of the other of the two transmissions relative to the gear shift of the one.
Thus, according to the prior art automatic transmission, the opposite direction gear shift detecting means, the delay time setting means and the gear shift command outputting means are required, and both of the main transmission and the sub-transmission have to be controlled. Consequently, the number of factors to be controlled when shifting gears is increased, and the control becomes extremely complicated, leading to high production costs.
The present invention was made in view of these situations, and an object thereof is to provide an automotive automatic transmission in which the number of factors to be controlled when shifting gears is reduced and a control system therefor can be simplified, thereby making it possible to attempt to reduce the production costs.
With a view to attaining the object, according to a first aspect of the invention, there is provided an automotive automatic transmission including a primary transmission mechanism having an input shaft connected to an engine, a planetary gear set which is constructed through mesh engagement of a sun gear, planetary gears and a ring gear which are each a helical gear, wherein one of the sun gear and the ring gear is connected to the input shaft and the other is connected to a one-way clutch via a stationary member and wherein a carrier for the planetary gears is connected to a primary output shaft, and a centrifugal clutch adapted to engage the input shaft with the primary output shaft in correspondence with a centrifugal force by a weight and to release the input shaft from the primary output shaft through a thrust force by the helical gears, and a secondary transmission mechanism connected to the primary output shaft of the primary transmission, for controlling to shift gears into two or more speed-changed conditions. The automotive automatic transmission includes a gear shift controlling unit for selectively combining a released state and an engaged state of the centrifugal clutch of the primary transmission mechanism for each of the speed-changed conditions of the secondary transmission mechanism to thereby establish a multiplicity of change-speed gears.
Because the centrifugal clutch of the primary transmission mechanism is adapted to be engaged in correspondence with the centrifugal force by the weights and to be released by virtue of the thrust force of the helical gears, the gear shift conditions by the planetary gear set can automatically be changed over.
Consequently, since the primary transmission automatically selects a gear shift condition according to the driving condition by controlling only the secondary transmission mechanism for shifting gears, the number of factors to be controlled in shifting gears can be reduced, whereby the control system can be simplified, resulting in a reduction in production costs.
According to a second aspect of the present invention, there is provided an automotive automatic transmission as set forth in the first aspect of the invention, wherein a torque converter is provided between the engine and the input shaft and wherein a neutral condition of the automatic transmission is produced by cutting off the transmission of power in the secondary transmission mechanism by the gear shift controlling unit.
The torque converter is set without any additional specific mechanism such as a clutch for accelerating from a standstill in order to produce the neutral state in the automatic transmission, and therefore, a smooth acceleration from a standstill can be attained. In addition, the range of the ratio can be reduced by using the torque amplifying function of the torque converter, thereby making it possible to attempt to reduce the shock generated when shifting gears.
According to a third aspect of the invention, there is provided an automotive automatic transmission as set forth in the first or second aspect of the present invention, wherein the primary output shaft is made to be a hollow shaft so that the primary output shaft is disposed on an outer circumference of the input shaft in a concentric fashion, wherein the secondary output shaft is disposed in parallel with the primary output shaft, wherein the secondary transmission mechanism is constituted by a train of a plurality of gears provided between the primary output shaft and the secondary output shaft, and wherein a differential gear connecting to left and right wheels is allowed to connect to an axial end of the secondary output shaft which faces the engine.
The secondary transmission mechanism can be disposed between the engine connected to the input shaft and the primary transmission mechanism connected to the primary output shaft by disposing the output shaft which is made to be a hollow shaft on the outer circumference of the input shaft concentrically, and the differential gear can be disposed at the transversely central position of the vehicle by the secondary output shaft which is made shorter by allowing the differential gear to connect to the secondary output shaft which is in parallel with the primary output shaft at an end of the secondary output shaft which faces the engine.